1. Technical Field
The present invention relates to a solar cell and a manufacturing method thereof.
2. Description of the Related Art
A solar cell converts photons into electrical energy by use of characteristic of a semiconductor. The solar cell obtains energy from a reverse operation of a light emitting diode (LED) or a laser diode, which converts electrical energy into light energy. The solar cell technology has been steadily developed and some systems related to the solar cell have been commercialized or are now being rapidly commercialized.
The solar cell is basically a p-n junction diode. There are various kinds of the solar cells, based on their material used for a light absorption layer. A solar cell using silicon as the light absorption layer includes a crystalline (polycrystalline only) wafer type solar cell and a thin-film (crystalline, amorphous) solar cell. In addition, a CdTe or CIS (CuInSe2) compound thin-film solar cell, a III-V group solar cell, a dye-sensitized solar cell and an organic solar cell can be recommended as a representative solar cell.
The biggest problem faced by the photovoltaic power generation technology is the high cost of power generation caused by the high price of the system. The problem acts as the biggest obstacle to the wide spread of the photovoltaic power generation technology. Considering that a silicon substrate solar cell (polycrystalline only) has a market share of more than 90%, it can be understood that the present high price of the photovoltaic power generation system is caused by the high price of solar modules, i.e., high price of silicon substrates constituting the solar cell. Accordingly, it is possible to remarkably reduce the high prices of the solar cell and the system by manufacturing an element by depositing minimum materials required for manufacturing the solar cell on an inexpensive substrate in the form of a thin film, instead of the silicon substrate, which is a main factor of the high system price.
Major thin-film solar cells include the silicon-based solar cell, the CuInSe2-based solar cell and the CdTe thin-film solar cell, depending on the light absorption layer material. Such thin-film solar cells have an advantage of using an inexpensive substrate such as a glass plate or a metal plate instead of the expensive silicon substrate, and of being manufactured at a low cost by consuming a minimum amount of materials through the deposition of a thin film having thickness of about several micrometers. It is possible to improve the productivity and lower the price by manufacturing a wide-area module through the use of an in-line process.
A solar cell using a glass plate is shown in FIG. 1 as an example of a silicon thin-film solar cell. A glass plate 1 is used as a substrate, and a transparent conductive oxide 2 is deposited on one surface of the glass plate 1. Subsequently, an n-type semiconductor 3 and a p-type semiconductor 4 are successively deposited so that a p-n junction is made. A light beam is incident on the surface of the glass plate 1 and passes through the transparent conductive oxide 2 and the n-type semiconductor 3. Then, the light beam is absorbed by the p-type semiconductor 4. In this case, an electromotive force causes an excited electron to flow, and then electric power can be obtained.